But that was is the point of the Death Star map, the rebels should be under a lot of fire, I mean they're assaulting an IMMENSE battle station that is equiped with thousands of turbolasers and tons of TIEs.  That is the purpose for making the trench run, if you don't stay in the trench, then you get blasted to little bits by the turbolasers on the surface. 

As for a UAV on the death star map, I'm not sure how well that would fit into the one-way objective style play.  And I don't think that the Imps would be using probe droids out there anyway.  Maybe neither side gets a UAV, but instead the Commander's scan function recharges very fast.  This would also improve the teamplay, for instance, the TIE fighter pilots would have to rely on the commander or other teammates to relay position information on the incoming rebel fighters.

And I believe that there was a whole fleet of star destroyers at Hoth, including of course Vader's personal Super SD, the Executor.  Since regular ISDs only carry landing barges with enough room for one ATAT in each, I'm thinking that the Executor launched its Y-85 barges to deploy the ground force.